This proposal is designed to investigate the biochemical mechanisms underlying hippocampal long-term potentiation (LTP), a form of synaptic plasticity thought to be a cellular substrate for mammalian learning and memory processes. I have previously shown, using a sensitive and selective biochemical assay, that LTP is associated with an increase in protein kinase C (PKC) activity in both the induction and maintenance of LTP. Little is known, however, about the mechanisms responsible for this LTP- associated increases in PKC activity. Oxygen free radicals are thought to contribute to the degeneration of neurons in a number of neuronal and brain diseases, including amyotrophic lateral sclerosis and Alzheimer's disease. Historically, these reactive oxygen species (ROS) have been thought to be toxic agents that disrupt normal cellular function. However, recent work suggests that some of these compounds may be involved in normal neuronal function as cellular messengers. Recent studies suggest that the oxygen free radical nitric oxide (NO) may be involved in the induction of LTP. The molecular targets for the action of this and/or other ROS are largely unknown. I propose to investigate interactions of ROS with PKC during induction of LTP. Using a combination of physiological and biochemical methods, I propose to l) to test the hypothesis that the increase in cofactor-dependent PKC activity associated with the induction of LTP is mechanistically different from the increase in cofactor-independent PKC activity associated with the maintenance of LTP, 2) to test the hypothesis that PKC is activated by ROS after LTP-inducing stimuli and determine the ROS that activates PKC, 3) to test the hypothesis that the ROS that activates PKC is necessary in the junction of LTP, 4) to test the hypothesis that the induction and maintenance phases of LTP are associated with increased phosphorylation of PKC substrates in situ. The combination of electrophysiological, pharmacological, and biochemical techniques affords the opportunity to address these questions. These studies should result in a more thorough understanding of how long-term alterations in neuronal function are regulated by oxygen free radicals. They should provide insight on how alterations in one of these naturally occurring processes could result in neuronal and brain dysfunction manifested in diseases such as amyotrophic lateral sclerosis and Alzheimer's disease.